1. Field of the Invention
The present invention relates to data exchange, and in particular to data exchange synchronization between a local member and a remote member.
2. Description of Related Art
In general, a local member has a reference clock signal which is transmitted to a remote member in order to participate in an exchange of data with the remote member.
The problem is that the remote member receives the reference clock signal with a certain delay with respect to its generation in the local member. This delay means that the clock signals in the local member and in the remote member are no longer in phase.
For example, the local member can be a memory controller housed in an integrated circuit and the remote member can be a synchronous memory such as an SDRAM memory. The integrated circuit which houses the memory controller and the integrated circuit which houses the memory are placed on a printed circuit, connected by tracks having resistive, capacitive and inductive properties suitable for generating a certain delay on the transmitted signals. At the ever higher frequencies for exchange between the circuits, these delays have a considerable effect on the synchronization of signals.
One solution to this problem is to deliberately introduce a delay in the local member before transmission of the clock signal and to adjust this delay so as to compensate for the uncontrollable delay outside the integrated circuit which houses the local member, so that the clock signal in the remote member has a phase suitable for ensuring the synchronization of the exchange of data.
Typically, the signal subjected to the uncontrollable external delay is looped back on the reference clock signal at the input of a phase comparator. The delay introduced into the local member is adjusted so as to cancel out the phase difference at the input of the phase comparator. One drawback of this solution is that it only allows the delay on the signal subjected to the uncontrollable external delay to be controlled by cancelling out the phase difference at the input of the comparator. Such a solution presents problems when the data, for example generated by the remote member, are valid within a window of validity, that is to say within a range which precedes, succeeds or is superimposed on the clock wavefront. It is then difficult to impose a phase difference other than a zero value at the input of the phase comparator.